Re: [PATCH] virtio-blk: emit udev event when device is resized

Milos Vyletel
2013-02-25T23:41:12Z

On Feb 25, 2013, at 5:12 PM, Greg KH <greg@kroah.com> wrote:

> On Fri, Feb 22, 2013 at 10:14:49AM +1030, Rusty Russell wrote:
>> Milos Vyletel <milos.vyletel@sde.cz> writes:
>>
>>> When virtio-blk device is resized from host (using block_resize from QEMU) emit
>>> KOBJ_CHANGE uevent to notify guest about such change. This allows user to have
>>> custom udev rules which would take whatever action if such event occurs. As a
>>> proof of concept I've created simple udev rule that automatically resize
>>> filesystem on virtio-blk device.
>>>
>>> ACTION=="change", KERNEL=="vd*", \
>>> ENV{RESIZE}=="1", \
>>> ENV{ID_FS_TYPE}=="ext[3-4]", \
>>> RUN+="/sbin/resize2fs /dev/%k"
>>> ACTION=="change", KERNEL=="vd*", \
>>> ENV{RESIZE}=="1", \
>>> ENV{ID_FS_TYPE}=="LVM2_member", \
>>> RUN+="/sbin/pvresize /dev/%k"
>>
>> This looks fine to me, but I like to check with Greg before adding udev
>> callouts.... Greg?
>
> Hm, I thought we were frowning apon running binaries from udev rules
> these days, especially ones that might have big consequences (like
> resizing a disk image) like this.
>
> Kay, am I right?
>
> We already emit KOBJECT_CHANGE events when block devices change, from
> within the block core code. Why is the patch below needed instead of
> using these events that are already generated? How are virtio block
> devices special?
>
>> BTW, if this is good, it's good for stable IMHO.
>
> What bug does it fix?
>

It is not really a bug but it definitely is useful enhancement to have in stable too. I
can imagine lots of people can benefit from this.

Milos

> thanks,
>
> greg k-h
>
>> Cheers,
>> Rusty.
>>
>>> Signed-off-by: Milos Vyletel <milos.vyletel@sde.cz>
>>> ---
>>> drivers/block/virtio_blk.c | 3 +++
>>> 1 files changed, 3 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
>>> index 8ad21a2..5990382 100644
>>> --- a/drivers/block/virtio_blk.c
>>> +++ b/drivers/block/virtio_blk.c
>>> @@ -539,6 +539,8 @@ static void virtblk_config_changed_work(struct work_struct *work)
>>> struct virtio_device *vdev = vblk->vdev;
>>> struct request_queue *q = vblk->disk->queue;
>>> char cap_str_2[10], cap_str_10[10];
>>> + char event[] = "RESIZE=1";
>>> + char *envp[] = { event, NULL };
>>> u64 capacity, size;
>>>
>>> mutex_lock(&vblk->config_lock);
>>> @@ -568,6 +570,7 @@ static void virtblk_config_changed_work(struct work_struct *work)
>>>
>>> set_capacity(vblk->disk, capacity);
>>> revalidate_disk(vblk->disk);
>>> + kobject_uevent_env(&disk_to_dev(vblk->disk)->kobj, KOBJ_CHANGE, envp);
>>> done:
>>> mutex_unlock(&vblk->config_lock);
>>> }
>>> --
>>> 1.7.1